JAIC 2001, Volume 40, Number 1, Article 5 (pp. 59 to 68)
JAIC online
Journal of the American Institute for Conservation
JAIC 2001, Volume 40, Number 1, Article 5 (pp. 59 to 68)




The tests indicate that the tack is caused by the nature of Regalrez 1094 and not by the solvents or other additions. A recent product data sheet issued by Hercules gives Regalrez 1094 a Tg of 33C (Hercules 1998c). The Tg measured by de la Rie and McGlinchey (1990, 168) is 43.8C. The difference may be due to the methods used or to a change in the product. As we found, 33C is also the temperature at which Regalrez 1094 gets tacky. Nevertheless the Tg alone is not enough to explain why a polymer is sticky at a certain temperature. Long molecules, intermolecular forces such as hydrogen bonds, and cross-linking are among the most important reasons many polymers with an even lower Tg are not sticky at 33C (Horie 1994). Conversely, Regalrez 1094 has small molecules and few intermolecular forces, and it does not cross-link. These characteristics probably explain its tackiness at a relatively low temperature.

A varnish that gets tacky around 33C might not be a serious drawback for paintings if the varnish is not touched and if the painting is kept in a climatecontrolled room. On the other hand, Horie (1994, 18-20) states that the effective Tg is much lower when measured over a period of one year or more. This finding means that dust pickup could result even with temperatures below 33C. Dust pickup is actively taking place on the bed discussed at the beginning of this article, even though the temperature in the room has never reached 33C. From these observations it seems that Regalrez 1094 is not a suitable top finish. To benefit from the good qualities of Regalrez, the use of the higher grade of Regalrez 1126 is discussed below.

Copyright 2001 American Institution for Conservation of Historic & Artistic Works